Cold engine does not run smoothly

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jakiidd
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Cold engine does not run smoothly

Post by jakiidd »

Hello!

Sorry for my english in advance =)

I have the new WLTP Polo GTI car for exactly one month. I made 1500 km with it.

I noticed that every time the car is totally cold and when driving it for the first minute or two, it does not work smoothly. Even if I always have the same pressure on the throttle, the car once accelerates the next time it doesn't, and then changes to the next gear and back to the previous, etc. After I do an acceleration of more than 60+ km/h the car works perfectly ... When the car is warm and I turn it off and on again after a few minutes it works perfectly, but if I let it stay for like more than an hour it is the same as all the mornings. We have from 0 - 10 degrees. I feel like I am driving a 20 years old car for the first minute every morning ...

Anyone having the same issue ?

Another thing is very interesting. The coolant water in the car gets 90 degrees in 5 minutes (4km). The oil gets 90 degrees in 10 min (10km). That is impressivly quick.

Also, in the first 3 kilometers I can not get an avg less than 9l/100km. In 10km I already get an avg. of 7,5l/100km and if I do more than 15km I get 6,5l/100km. I drive on very open roads and with very little or none traffic with speeds
around 50-90 km/h.

Can someone tell me what are the differences between a WLTP and pre WLTP GTI ?

Let's hope they crack the ECU for us so that we will be able to remove the GPF and tune it =)

Regards!
monkeyhanger
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Re: Cold engine does not run smoothly

Post by monkeyhanger »

jakiidd wrote: Sat Feb 02, 2019 8:27 pm Hello!

Sorry for my english in advance =)

I have the new WLTP Polo GTI car for exactly one month. I made 1500 km with it.

I noticed that every time the car is totally cold and when driving it for the first minute or two, it does not work smoothly. Even if I always have the same pressure on the throttle, the car once accelerates the next time it doesn't, and then changes to the next gear and back to the previous, etc. After I do an acceleration of more than 60+ km/h the car works perfectly ... When the car is warm and I turn it off and on again after a few minutes it works perfectly, but if I let it stay for like more than an hour it is the same as all the mornings. We have from 0 - 10 degrees. I feel like I am driving a 20 years old car for the first minute every morning ...

Anyone having the same issue ?

Another thing is very interesting. The coolant water in the car gets 90 degrees in 5 minutes (4km). The oil gets 90 degrees in 10 min (10km). That is impressivly quick.

Also, in the first 3 kilometers I can not get an avg less than 9l/100km. In 10km I already get an avg. of 7,5l/100km and if I do more than 15km I get 6,5l/100km. I drive on very open roads and with very little or none traffic with speeds
around 50-90 km/h.

Can someone tell me what are the differences between a WLTP and pre WLTP GTI ?

Let's hope they crack the ECU for us so that we will be able to remove the GPF and tune it =)

Regards!
My pre-WLTP GTI+ runs a little roughly below 10mph (16kmph) when I am driving along and out of my employer's car park with a cold engine in 1st and 2nd gear. Driving into the car park at the end of my 13 mile (21km) commute to work with a warm engine is fine. Once I leave the car park to go home and go straight onto a 30mph (48kmph) road, the rough running is gone.

My car's water gets to 90C in 2 miles (3km), with the oil being up to 90C in 6 miles (10km) - that's very quick for the water, and about the same as my Golf R for the oil.

It takes about 6 miles (10km) for my pre-WLTP GTI+ to get to 31mpg (miles per gallon), which is equivalent to 9l/100km. You're averaging 38mpg (7.5l/100km) which is about what I can do on my commute if the traffic is very light (during the school holidays, when not so many people are commuting to work). Average on my commute is 34mpg (8.3l/100km).

The best I have done is 100 miles (161km) from Newcastle to York, mainly maintaining 80mph (129kmph) on a clear motorway and the journey averaged 43mpg (6.6l/100km). On the same journey,, but maintaining 60mph (97kmph), I'd expect to average 50mpg (5.9l/100km).

Those figures seem to tie in with yours quite well, indicating that you are no worse off for having a DPF.

As far as I can tell, the only difference between pre-WLTP and post-WLTP Polo GTI is that pre-WLTP GTI has no GPF. The engine seems exactly the same - after it was confirmed that MPI has not been lost with WLTP compliance has (unlike the Golf GTI variant of the same engine which is now direct injection only, not DI + port injection.
CBjergfelt
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Re: Cold engine does not run smoothly

Post by CBjergfelt »

Hi, did you ever solve your issue.

I have the excatly same problem
monkeyhanger
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Re: Cold engine does not run smoothly

Post by monkeyhanger »

CBjergfelt wrote: Tue Oct 20, 2020 6:22 pm Hi, did you ever solve your issue.

I have the excatly same problem
It's a characteristic of the engine when running cold under extremely low loads (presumably running the Budack cycle/port injection.
john M
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Re: Cold engine does not run smoothly

Post by john M »

Re coolant temp rapid rise, all vws for the past 20 years or so in my experience will indicate 90C between actual coolant temperatures of approx 75c and 107C, this is why you never see the temperature changing even when the cooling fan cuts in.
Andy Beats
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Re: Cold engine does not run smoothly

Post by Andy Beats »

Now that we're into cold mornings up here, I can confirm my GTi runs a bit 'weird' when cold.
It's not misfiring or stuttering, it's more like surging.
tom.wright
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Re: Cold engine does not run smoothly

Post by tom.wright »

Mine does this too. I think it's to do with being in first gear as well. My last car was very similar when cold and in first gear, and the Polo has a very low first.

It's smoother once it changes into second.
Andy Beats
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Re: Cold engine does not run smoothly

Post by Andy Beats »

tom.wright wrote: Mon Oct 26, 2020 12:12 pm Mine does this too. I think it's to do with being in first gear as well. My last car was very similar when cold and in first gear, and the Polo has a very low first.

It's smoother once it changes into second.
Mine isn't restricted to first gear.
I get the slight 'surging' all through the village at 30mph when cold, which is at least third gear - possibly fourth.
tom.wright
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Re: Cold engine does not run smoothly

Post by tom.wright »

Andy Beats wrote: Mon Oct 26, 2020 12:22 pm Mine isn't restricted to first gear.
I get the slight 'surging' all through the village at 30mph when cold, which is at least third gear - possibly fourth.
Hmm.. then I'm not sure. I have noticed mine holds on to the gears longer when it's cold which makes it a bit jumpy, but not as you describe.
Andy Beats
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Re: Cold engine does not run smoothly

Post by Andy Beats »

tom.wright wrote: Mon Oct 26, 2020 12:32 pm Hmm.. then I'm not sure. I have noticed mine holds on to the gears longer when it's cold which makes it a bit jumpy, but not as you describe.
It's certainly jumpy in first when cold, I unexpectedly went wheelspinning out of the street on Saturday.
The surging I get in higher gears when cold isn't hugely pronounced, it's just like I'm very gently going on/off the throttle, when I'm not.
it's noticeable to me, it's not neck jerking stuff.
Last edited by Andy Beats on Tue Oct 27, 2020 5:37 pm, edited 1 time in total.
john M
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Re: Cold engine does not run smoothly

Post by john M »

It would be interesting to see what effect, if any, that a thermostatically controlled heated air intake wold have, a throwback to the carburettor days although my first MPI car, a 2000 Bora, did have one, both a family 2005 and a 2018 Polo are a bit hesitant for a few minutes in very cold weather, also I think they go into closed loop at a coolant temp of ~ 30C.
Andy Beats
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Re: Cold engine does not run smoothly

Post by Andy Beats »

Wonder if 'fancy' petrol might make a difference.
monkeyhanger
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Re: Cold engine does not run smoothly

Post by monkeyhanger »

Andy Beats wrote: Tue Oct 27, 2020 5:43 pm Wonder if 'fancy' petrol might make a difference.
Wouldn't make any odds unless it was pinking when cold (which it isn't). As you said earlier, the lumpiness feels like surging. I'd agree that it feels like that, but is really short lived and only at really low speeds when the engine is stone cold. I used to have it happen when crawling out of the works car park at less than 10mph.

I suspect the engine is flitting between port injection and direct injection while cold when this happens, but it's definitely not pinking and both the 2018 non-GPF and 2019 GPF GTI+ suffer from it, regardless of fuel type/brand.

Higher RON fuels are for higher output engines that need more fuel at max output than can be supplied as RON95 fuel without pinking. The threshold is usually around the 280ps mark for VAG 2.0TSI engines. The Golf R's engine is 300/310ps with RON97-99 fuel, but downrates to 285ps through retarded timing when the antiknock sensor detects pinking through use of RON95 fuel.

I'd expect some of these remapped Polo GTIs running 280ps might benefit from running RON99 fuel to prevent pinking.
Andy Beats
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Re: Cold engine does not run smoothly

Post by Andy Beats »

monkeyhanger wrote: Tue Oct 27, 2020 6:50 pm
Andy Beats wrote: Tue Oct 27, 2020 5:43 pm Wonder if 'fancy' petrol might make a difference.
Wouldn't make any odds unless it was pinking when cold (which it isn't). As you said earlier, the lumpiness feels like surging. I'd agree that it feels like that, but is really short lived and only at really low speeds when the engine is stone cold. I used to have it happen when crawling out of the works car park at less than 10mph.

I suspect the engine is flitting between port injection and direct injection while cold when this happens, but it's definitely not pinking and both the 2018 non-GPF and 2019 GPF GTI+ suffer from it, regardless of fuel type/brand.

Higher RON fuels are for higher output engines that need more fuel at max output than can be supplied as RON95 fuel without pinking. The threshold is usually around the 280ps mark for VAG 2.0TSI engines. The Golf R's engine is 300/310ps with RON97-99 fuel, but downrates to 285ps through retarded timing when the antiknock sensor detects pinking through use of RON95 fuel.

I'd expect some of these remapped Polo GTIs running 280ps might benefit from running RON99 fuel to prevent pinking.
This is true about fancy fuels, but I've noticed the effect it can have it normal cars in positive and negative ways.
For example, fancy diesel in my Audi A3 2.0tdi was horrible, it made it completely unable to hold a steady 40mph, the car was surging like you had an itchy foot.
But the same fuel in a BMW diesel resulted in much smoother running.
I might give it a go, it may be that the fuel/air mixture is just far too lean when cold and the higher octane rating may counteract that.
The fact the car does take a while to warm up for a petrol also points towards a lean cold mixture.
monkeyhanger
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Re: Cold engine does not run smoothly

Post by monkeyhanger »

Fancy fuel won't counteract that. There's a common misconception that higher octane petrol is more energy dense than regular RON95 - it isn't. Many higher octane fuels up the octane number by diluting with Ethanol (pure ethanol has an octane number of 108, but is about 10% less energy dense than petrol). You won't get a less lean mix by adding the same amount of RON99 in.

Under very low loads (like me crawling out of the car park under 10mph), the Budack cycle is operating a very lean mix under a higher effective compression ratio. Put your footdown enough to not be running on the Budack cycle (about 20kW) and the lumpiness experienced when the car is stone cold disappears. It seems then that VW could easily eliminate this with software updates to prevent the car running Budack cycle while cold.

The difference between RON95 and RON97/98/99 is additives that make the petrol less volatile and more compressible before autoignition (pinking) occurs. This helps higher output engines that require more fuel to realise their upper output. You can put more fuel in without pinking or you can compress the same amount of fuel further without pinking.

My A4 190TDI runs more efficiently with a cetane enhancer- I add about 80mL of Millers to every tank and the fuel economy is up about 7%. I filled up on Sunday and forgot to put the additive in. We went to Bamburgh on Monday, a 100 mile round trip, and only got 47mpg. I put the Millers in on Monday night and went to Alnwick/Alnmouth yesterday (pretty much the same route, just 8 miles shorter up the A1) and got 52mpg.

Almost conversely to RON numbers, a high cetane number makes the diesel a little more volatile, so it ignites slightly easier under compression, making for a more complete burn, less soot and a cleaner DPF.

Whether it be Cetane boosters or higher RON fuel, the calorificcontent of the fuel doesn't appreciably change with the additives, the volatility of the fuel does.
Last edited by monkeyhanger on Wed Oct 28, 2020 11:08 am, edited 1 time in total.
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